PSI - Issue 30

Kirill Kurgan et al. / Procedia Structural Integrity 30 (2020) 53–58 Kirill Kurgan et al. / Structural Integrity Procedia 00 (2020) 000–000

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The next step was to study the mechanical properties of the welded sample. Its stress-strain curve is shown in Fig. 2, b and d . The metal microplasticity for the welded sample, as for the steel one, also begins at a strain of about 0.35% (Fig. 2, d). At a strain of 2.1% and a stress of 300 MPa, the yield point was observed, but it was short enough (about 1%). For comparison, it had been 2.5 times longer for the high-strength low-alloy steel 0.9%C-2%Mn-1%Si. As a rule, the yield point presence on the  (  ) curves had been due to the development of localized plastic strains because of the movement of the Chernov-Luders bands according to Gorbatenko et al. (2018). However, they were absent in the distribution patterns of the stain fields in the studied case (Fig. 4, pattern 3) due to the  strain induced phase transformations in the heat-affected zone and the weld metal. It had been shown in that the  phase transformations had occurred in the steel 0.12%C-18%Cr-10%Ni-1%Ti under tensile loads, while welding had not resulted in the elastic crystal lattice distortion and the microcrack formation. In the studied case, the  strain-induced phase transformations had damped the strain energy in the weld metal and affected the distribution of the strain fields at all four stages according to Fig. 2. This fact was confirmed by the obtained patterns of the localization of the plastic strains at different stages (Fig. 4, patterns 4–8).

Fig. 4. The distribution patterns of the longitudinal strain fields  yy on the welded sample surface: 1)  =0.2%; 2)  =0.7%; 3)  =3.7%; 4)  =8.7%; 5)  =11.4 %; 6)  =24.0%; 7)  =31.0%; 8)  =38.0%. These patterns correlate with the points 1  8 on the stress-strain curve shown in Figure 2, b